A new video that shows a German shepherd trying valiantly -- and successfully -- to keep authorities from its injured friend on one of the busiest highways in New York City is just the latest example of dogs who go above and beyond to protect their loved ones.

"It's possible ... there was a social bond," said Dr. E'Lise Christensen, a veterinarian and board certified animal behaviorist.

The apparent German shepherd mix in New York City kept officials at bay on the Major Deegan Expressway by running frantic circles around the injured dog, which lay motionless and bleeding in the middle of the road. If officers tried to approach the injured animal, the shepherd would lunge, warning them to stay away.

Christensen, who works for Manhattan-based New York City Veterinary Specialists, said after watching video of the dogs, the shepherd's protection of his injured companion was "really serious."

"All we know is he's using these barking and lunging behaviors to get people to go away," she said.

In the end, officers were able to grab the injured dog which was treated by veterinarians. ABC's New York affiliate WABC reported that both dogs, which live together in the Bronx, were claimed by their owner and that the shepherd is the injured dog's offspring.

The video bore similarities to another canine highway hero from Chile. In December, cameras captured a dog's bold move to drag another dog to the side of the road after it had been struck on a busy highway.

The video shows the heroic dog dodging fast-moving traffic to reach its friend and then back again, this time dragging the dead pooch.

Dogs aren't always loyal only to their own kind.

Last summer, a mixed breed dog named China was hailed as a life saver in Argentina when she saved a newborn child from what doctors said would have been certain death.

China found the infant in a field where it had been abandoned by its 14-year-old mother. China, according to local reports, brought the baby back to her litter of six puppies and kept it warm until her owner found the expanded family and called authorities.

Understanding Dog Behavior

While these dogs have found acclaim on news sites and viral videos, Christensen said people need to remember that it's nearly impossible in many cases to know exactly what the dogs' motivation was during the incidents that led them to be labeled as heroes.

People, she said, tend to project human emotions onto animals, but no one really knows if animals have altruistic tendencies.

"We start to think, 'How complex is their inner thought process?" she said.

In the case of the Argentine dog who rescued the baby, Christensen said, her behavior is easier to explain.

"Female dogs can perform maternal behaviors to non-puppies," she said, noting they are driven by both hormones and instinct.

Even though a dog willing to bring a human infant into her brood may be unusual, she said, it's "not beyond the scope of possibility."

A Florida family thanked their dog Penny in August when she chased a 200-pound bear up a tree after it ventured onto the family's property.

And last December, a New York family's pit bull mix, Kola, was presumed kidnapped after chasing intruders from her family's New City home. Kola, who had been adopted after being saved from a Yonkers, N.Y., dog fighting ring, according to New York affiliate WABC, was found tied to a signpost in New Jersey, injured, but safe.

Kola's owners, the Rosen family, told WABC that she had gone after the intruders when they tried to break in through a window. She chased them off the property, but then vanished.

Christensen said many dogs excel at identifying threats and protecting their "pack." Some breeds, including dobermans, German shepherds and rottweilers, have been bred specifically for that purpose.

While dogs like Penny are hailed as heroes, she said, that instinct can sometimes backfire when dogs feel the need to "protect" their owners and territory from things like the mailman or the Chinese food delivery guy.

"Every dog's an individual [in] what they're going to be willing, able and interested in doing in any given situation," Christensen said.